Compliant hydrodynamic gas journal bearings are being used in high performance machinery subject to extreme conditions of temperature and speed. These bearings are ideally suited for these conditions because they do not suffer from the speed and durability limitations of rolling element bearings. Also, they do not require oil lubrication and therefore are free of the temperature limitations of oil. In addition, the oil seals and the pumping, cooling and filtering equipment necessary for use in oil bearings are rendered unnecessary, thereby producing a significant weight and cost saving which is desirable, especially in aviation applications.
The compliant hydrodynamic journal bearing employs a composite bearing assembly including a resilient supporting element and an attached overlying bearing sheet. This composite bearing lines the surface of the journal sleeve and is in bearing relationship to the shaft surface. Briefly, the theory of this bearing posits a hydrodynamic supporting gas film generated by the relative movement of the shaft surface over the bearing sheet to support the shaft on a thin cushion of gas over the bearing sheet. The compliance of the supporting element underlying the bearing sheet enables it to deflect to assume the optimum shape relative to the shaft surface to produce the maximum supporting fluid pressure and distribution. It also enables the bearing sheet to conform, to some extent, to misaligned, unbalanced, and thermally distorted shafts.
Despite the proven advantages that the use of these bearings confer, we have recognized certain potential advantages which may accrue from a refinement of these bearings for certain applications such as ground vehicles and particularly in aviation applications. High speed rotating machinery experiences a strong gyroscopic effect during deviation from straight-line motion, causing strong transaxial forces to be exerted on the bearings. These forces are proportional to the moment of inertia of the rotor, the rotation speed of the rotor, and the angular velocity of vehicle executing the maneuver. Increasing the rotor speed, and the speed and maneuverability of the vehicle increases these forces to the extent that, during certain evasive movements of high performance fighter aircraft, for example, the forces can exceed the load capacity of the bearing.
Failure can occur in misaligned shafts supported by compliant hydrodynamic fluid bearings when the fluid film between the relatively rotating parts is unable to carry the load tending to force those parts together. When this happens, the metal surfaces come into contact at high rotational speeds causing damage to the bearing.